The Experts below are selected from a list of 120 Experts worldwide ranked by ideXlab platform
J A Tabares - One of the best experts on this subject based on the ideXlab platform.
-
magnetic properties of the fexmn0 600 xal0 400 0 200 x 0 600 Disordered Alloy series
Journal of Physics: Condensed Matter, 2002Co-Authors: Ligia E Zamora, J A Tabares, Claudia Gonzalez, German Antonio Perez Alcazar, J M GrenecheAbstract:The magnetic properties of the FexMn0.600 −xAl0.400(0.200 ≤ x ≤ 0.600) Disordered Alloys were investigated by means of Mossbauer spectrometry, ac magnetic susceptibility, and ac calorimetry measurements. Our results are summarized in a magnetic phase diagram, which includes an antiferromagnetic phase for x ≤ 0.300 at T ≤ 225 K, a ferromagnetic one for x ≥ 0.425 at T ≤ 340 K, and a paramagnetic phase for high temperatures and all the compositions. This phase diagram also shows for the first time both a re-entrant spin-glass–ferromagnetic transition line for x ≥ 0.425 and T ≤ 60 K and a re-entrant spin-glass–antiferromagnetic one for x ≤ 0.300 and T ≤ 40 K. The occurrence of superparamagnetic-like blocked events (for 0.300 ≤ x ≤ 0.600 and at T ≈ 200 K) is associated with the presence of Fe-rich magnetic clusters which can originate from the Disordered atomic character of the Alloys.
-
mossbauer evidence of reentrant spin glass phase in the fe0 45mn0 25al0 30 Disordered Alloy
Hyperfine Interactions, 1994Co-Authors: G Perez A Alcazar, A Bohorquez, J A Tabares, J R GancedoAbstract:Mossbauer effect measurements in Disordered Fe0.45Mn0.25Al0.30 Alloy from 15 to 300 K show it to be a reentrant spin-glass with a freezing temperatureTK near 60 K and a Curie temperatureTc near 250 K. The Mossbauer spectra show a paramagnetic site with a relative area that increases withT and this increase is abrupt near 60 K.
-
mossbauer and magnetization evidence of spin glass phase in the fe0 45mn0 25al0 30 Disordered Alloy
Journal of Magnetism and Magnetic Materials, 1994Co-Authors: Ligia E Zamora, G Perez A Alcazar, A Bohorquez, J A TabaresAbstract:Abstract A study by Mossbauer spectroscopy and magnetization of the Fe 0.45 Mn 0.25 Al 0.30 Disordered Alloy is reported. The curves of magnetization versus temperature for zero-filled cooling (ZFC) and field cooling (FC) are different above 60 K. Also, this Alloy showed a remanent magnetization and a temporal decrease when the field turns off. This spin-glass behavior was confirmed as a re-entrant spin-glass in the ferromagnetic phase by Mossbauer spectroscopy.
J R Gancedo - One of the best experts on this subject based on the ideXlab platform.
-
mossbauer evidence of reentrant spin glass phase in the fe0 45mn0 25al0 30 Disordered Alloy
Hyperfine Interactions, 1994Co-Authors: G Perez A Alcazar, A Bohorquez, J A Tabares, J R GancedoAbstract:Mossbauer effect measurements in Disordered Fe0.45Mn0.25Al0.30 Alloy from 15 to 300 K show it to be a reentrant spin-glass with a freezing temperatureTK near 60 K and a Curie temperatureTc near 250 K. The Mossbauer spectra show a paramagnetic site with a relative area that increases withT and this increase is abrupt near 60 K.
G Perez A Alcazar - One of the best experts on this subject based on the ideXlab platform.
-
bulk magnetic properties of the fe0 5mn0 1al0 4 Disordered Alloy a monte carlo study
Hyperfine Interactions, 2003Co-Authors: J Restrepo, G Perez A Alcazar, Claudia Gonzalez, O Arnache, J M GrenecheAbstract:In this work we present a simulational study of the bulk magnetic properties of the Fe0.5Mn0.1Al0.4 Disordered system. The magnetization per site, specific heat and magnetic susceptibility were obtained using Monte Carlo simulation. Simulation results were performed in the framework of a random site-diluted 3D Ising model with nearest neighbor interactions, and using a single-spin-flip Metropolis dynamics for equilibration and energy minimization, from which canonical ensemble and configurational averages were computed. In the simulation, atoms were randomly distributed on a body-centered cubic lattice in order to simulate the disorder and crystalline structure as obtained in the arc-melted Fe0.5Mn0.1Al0.4 Alloy treated at high temperatures for long periods of time and followed by fast quenching. Competitive Fe–Fe ferromagnetic and Fe–Mn and Mn–Mn antiferromagnetic interactions were taken into account, as well as the Al dilutor effect. We conclude that, accordingly with Mossbauer results, the Fe0.5Mn0.1Al0.4 system exhibits a reentrant spin-glass behavior below 30 K characterized by a sharp increase of the mean hyperfine field attributed to the magnetic ordering of the Mn sublattice at these temperatures. Additionally, a ferromagnetic to paramagnetic transition at around 300 K was also evidenced.
-
mossbauer evidence of reentrant spin glass phase in the fe0 45mn0 25al0 30 Disordered Alloy
Hyperfine Interactions, 1994Co-Authors: G Perez A Alcazar, A Bohorquez, J A Tabares, J R GancedoAbstract:Mossbauer effect measurements in Disordered Fe0.45Mn0.25Al0.30 Alloy from 15 to 300 K show it to be a reentrant spin-glass with a freezing temperatureTK near 60 K and a Curie temperatureTc near 250 K. The Mossbauer spectra show a paramagnetic site with a relative area that increases withT and this increase is abrupt near 60 K.
-
mossbauer and magnetization evidence of spin glass phase in the fe0 45mn0 25al0 30 Disordered Alloy
Journal of Magnetism and Magnetic Materials, 1994Co-Authors: Ligia E Zamora, G Perez A Alcazar, A Bohorquez, J A TabaresAbstract:Abstract A study by Mossbauer spectroscopy and magnetization of the Fe 0.45 Mn 0.25 Al 0.30 Disordered Alloy is reported. The curves of magnetization versus temperature for zero-filled cooling (ZFC) and field cooling (FC) are different above 60 K. Also, this Alloy showed a remanent magnetization and a temporal decrease when the field turns off. This spin-glass behavior was confirmed as a re-entrant spin-glass in the ferromagnetic phase by Mossbauer spectroscopy.
I Matsumoto - One of the best experts on this subject based on the ideXlab platform.
-
fermi surface of a Disordered cu al Alloy single crystal studied by high resolution compton scattering and electron diffraction
Physical Review B, 2004Co-Authors: J Kwiatkowska, N Shiotani, I Matsumoto, F Maniawski, H Kawata, S Kaprzyk, L Litynska, A BansilAbstract:We have measured high resolution Compton scattering profiles for momentum transfer along a series of 28 independent directions from ${\mathrm{Cu}}_{0.842}{\mathrm{Al}}_{0.158}$ Disordered Alloy single crystals with normals to the surfaces oriented along the [100], [110], and [111] directions. The experimental spectra are interpreted via parallel first-principles KKR-CPA (Korringa-Kohn-Rostoker coherent-potential approximation) computations of these directional profiles. The Fermi surface determined by inverting the Compton data is found to be in good agreement with the KKR-CPA predictions. An electron diffraction study of the present ${\mathrm{Cu}}_{0.842}{\mathrm{Al}}_{0.158}$ sample is additionally undertaken to gain insight into short-range ordering effects. The scattering pattern displays not only the familiar diffuse scattering peaks, but also shows the presence of weak streaks interconnecting the four diffuse scattering spots around the (110) reciprocal lattice points. This study provides a comprehensive picture of the evolution of the shape of the Fermi surface of $\mathrm{Cu}$ with the addition of $\mathrm{Al}$. Our results are consistent with the notion that Fermi surface nesting is an important factor in driving short-range ordering effects in Disordered Alloys.
-
two dimensional folding technique for enhancing fermi surface signatures in the momentum density application to compton scattering data from an al 3 at li Disordered Alloy
Physical Review B, 2001Co-Authors: I Matsumoto, N Shiotani, J Kwiatkowska, F Maniawski, M Itou, H Kawata, S Kaprzyk, P E Mijnarends, B BarbielliniAbstract:We present a technique for enhancing Fermi surface ~FS! signatures in the two-dimensional ~2D! distribution obtained after the 3D momentum density in a crystal is projected along a specific direction in momentum space. These results are useful for investigating fermiology via high-resolution Compton scattering and positron annihilation spectroscopies. We focus on the particular case of the ~110! projection in a fcc crystal where the standard approach based on the use of the Lock-Crisp-West ~LCW! folding theorem fails to give a clear FS image due to the strong overlap with FS images obtained through projection from higher Brillouin zones. We show how these superposed FS images can be disentangled by using a selected set of reciprocal lattice vectors in the folding process. The applicability of our partial folding scheme is illustrated by considering Compton spectra from an Al‐3 at. % Li Disordered Alloy single crystal. For this purpose, high-resolution Compton profiles along nine directions in the ~110! plane were measured. Corresponding highly accurate theoretical profiles in Al‐3 at. % Li were computed within the local density approximation~LDA!‐based Korringa-KohnRostoker coherent potential approximation ~KKR-CPA! first-principles framework. A good level of overall accord between theory and experiment is obtained, some expected discrepancies reflecting electron correlation effects notwithstanding, and the partial folding scheme is shown to yield a clear FS image in the ~110! plane in Al‐3 at. % Li.
-
a compton scattering study of an al li Disordered Alloy single crystal
Journal of Physics and Chemistry of Solids, 2000Co-Authors: I Matsumoto, Arun Bansil, J Kwiatkowska, F Maniawski, M Itou, H Kawata, S Kaprzyk, N ShiotaniAbstract:Abstract We report a measurement of the [111] Compton profile of a Disordered Al–3at.%Li Alloy single crystal at a high momentum resolution of 0.12 a.u., together with a corresponding highly accurate computation of the profile based on the Korringa–Kohn–Rostoker coherent-potential-approximation (KKR-CPA) scheme for treating disorder effects. In comparing the profiles and their first and second derivatives in Al–Li and Al, we find that the spectra in the Alloy differ systematically from those of Al in qualitative accord with the theoretical predictions. This study shows clearly that the high-resolution Compton technique is capable of probing delicate changes in the fermiology and electron correlation and bonding effects upon Alloying.
Deli Wang - One of the best experts on this subject based on the ideXlab platform.
-
phase conversion of pt3ni2 c from Disordered Alloy to ordered intermetallic with strained lattice for oxygen reduction reaction
Electrochimica Acta, 2018Co-Authors: Lingxuan Chen, Jing Zhu, Jie Wang, Weiping Xiao, Wen Lei, Tonghui Zhao, Ting Huang, Ye Zhu, Deli WangAbstract:Abstract Tuning the surface strain and atom arrangement to control the surface chemistry process is one of efficient strategies to enhance the electrocatalytic performance of nanomaterials. This research introduces an ordered Pt3Ni2/C intermetallic nanoparticle as a new type of the Pt-Ni system for the ORR, which is rarely reported at present. Besides, it focuses on the phase conversion of Pt3Ni2/C nanocatalysts from a Disordered phase to an ordered phase. X-ray diffraction (XRD) and transmission electron microscopy (TEM) measurements confirm the formation of ordered face-centered cubic (fcc) type Pt3Ni2/C nanocatalysts with homogeneous particle distribution and average crystallite size of 6.4 nm. The ordered fcc-Pt3Ni2/C exhibits improved electrocatalytic activities toward the oxygen reduction reaction (ORR) in 0.1 M HClO4 and 0.1 M KOH electrolyte when compared with Pt3Ni2/C Disordered Alloy. Besides, the robust ordered fcc-Pt3Ni2/C showed a smaller activity loss after durability tests in alkaline medium than acid electrolyte. The improved ORR activity and stability could be ascribed to the surface atom arrangement and reasonable surface strain originated from the ordered structure of Pt3Ni2/C nanoparticles relative to the Disordered Pt3Ni2/C Alloy, forcefully demonstrating that the Pt3Ni2/C intermetallic compound may act as highly efficient ORR electrocatalysts in energy conversion process.
-
structurally ordered intermetallic platinum cobalt core shell nanoparticles with enhanced activity and stability as oxygen reduction electrocatalysts
Nature Materials, 2013Co-Authors: Deli Wang, Huolin L Xin, Robert Hovden, Hongsen Wang, Yingchao Yu, David A Muller, Francis J Disalvo, Hector D AbrunaAbstract:Enhancing and optimizing the performance and durability of nanocatalysts for the oxygen reduction reaction is crucial for fuel-cell applications. A class of Pt–Co nanocatalysts consisting of ordered Pt3Co intermetallic cores with a 2–3 atomic-layer-thick platinum shell now exhibit a large increase in mass activity and specific activity when compared with Disordered Alloy nanoparticles.